Technical Field
The present invention relates to a writing instrument and an ink cartridge used for the same. Specifically, it relates to a writing instrument using a replaceable ink cartridge.
Background Art
Conventionally, for writing instruments having a built-in replaceable ink cartridge, an ink cartridge that directly stores ink in a container having one open end and has an opening blocked by a ball or a plug in a disk shape is widely used. In such ink cartridge, by engaging an ink-guidable tubular projection formed with a writing instrument body from a front end opening for connection, the plug is press-opened. When the plug is press-opened, ink in the ink cartridge is supplied to a pen point through the inside of the tubular projection (e.g., through hole). At this time, air is supplied from the pen point side into the container, thereby keeping the internal pressure of the ink cartridge in equilibrium to carry out stable ink supply (for example, refer to Patent Documents 3 and 4).
With a conventional tubular projection having a general purpose structure, it is difficult to let air enter the container and the ink supply is unstable. Then, attempts are made to form air intake paths inside the tubular projection (for example, refer to Patent Documents 1 and 2).
Patent Documents 1 and 2 describe writing instruments that have longitudinally extending slits formed in an inner circumferential wall of a tubular projection. The slits act as air intake paths. The slit-like air intake paths are intended to facilitate air flow into the ink cartridge. However, because the thickness of the wall portion constituting the tubular projection is thin, the slit-like air intake paths formed in the inner surface of the wall portion are fine. Further, the slit-like air intake paths continue to the through hole in the tubular projection to be an ink channel. The slit-like air intake paths are, therefore, prone to be in a fluid tight condition due to the ink. As just described, in the slit-like air intake paths, it is difficult to obtain a sufficient air flow because the fluid tight condition interferes with the inflow of air.
Patent Documents 3 and 4 describe writing instruments that have a configuration in which, when the plug is pressed, the ink cartridge is in a connected condition and the outer peripheral surface of the tubular projection air tight fits the inner circumferential surface of the opening of the ink cartridge. The tubular projection air tight fits the opening of the ink cartridge, thereby inhibiting ink leakage in the connected condition of the ink cartridge 6. Patent Document 4 also describes that, in addition to the air tight fitting configuration, locking bumps are provided on the outer peripheral surface of the opening of the ink cartridge and slitted locking portions are formed in the writing instrument body. Even when the air tight fitting turns out becomes looser over time, it is possible to inhibit ink cartridge drop-out by such locking bumps and slitted locking portions.
In the air tight fitting configuration described in Patent Documents 3 and 4, the tubular projection fits inside the opening of the ink cartridge, thereby forming the air tight condition. Therefore, the inner diameter of the through hole of the tubular projection that serves both as an ink channel and an air intake path turns out to be small. As a result, it is difficult to let air enter the ink cartridge and ink supply to the pen point side becomes unstable. In particular, when the outer diameter of the writing instrument is narrow, the ink cartridge and the outer diameter of the tubular projection are also narrow, so that the inner diameter of the through hole of the tubular projection turns out to be smaller. Therefore, in the writing instruments of Patent Documents 3 and 4, ink supply becomes more unstable.
The writing instrument described in Patent Document 4 also has a configuration in which, when the tubular projection air tight fits in the opening of the ink cartridge, the slitted locking portions of the writing instrument body fit over the locking bumps of the ink cartridge. When the ink cartridge is attached, the ink cartridge therefore does not deflect and thus requires a large pressing force. On the other hand, when the ink cartridge is detached, the ink cartridge has to be pulled out swiftly and there is a risk of causing scattering of residual ink and the like at that time.
Further, it is possible to repeatedly use the writing instruments described in Patent Documents 1 and 5 by replacing the empty ink cartridge after ink consumption.
The writing instruments described in Patent Documents 1 and 5 are provided with an intermediate member equipped with a tubular projection as a connecting portion to an ink cartridge. The intermediate member is fitted in the inner surface of a barrel that constitutes the writing instrument body. With the writing instrument described in Patent Documents 1 and 5, there is a risk that, when the empty ink cartridge is replaced, the intermediate member rotates together with the ink cartridge and that the intermediate member easily come out of the inner surface of the barrel.